DESCRIPTION

This invention relates to electric light devices both of incandescent type, normally known as "light bulbs" or lamps, and of discharge type, normally known as "fluorescent tubes". In particular, but not exclusively, we are concerned with such light devices where they are required or desired to give a coloured effect. Coloured lamps are, of course, well known having standard clear or pearl glass enclosures as made, but later coated, typically lacquered, to give the desired or required colours. The additional colouration step at manufacture, and presumably relatively low volumes involved, result in rather high prices to the customer, typically 30 pence to £1.00 more than for uncoloured bulbs. One alternative by way of using self-coloured glass is presumably yet more expensive, or it would be done by bulb manufacturers. Another possibility, by way of a separate enclosure after the manner of shades or diffusers, seems equally unsatis actory on cost, and seems inevitably to have some disadvantage in spacing

from the plain lamp at least for external use. Another matter of concern to us is the tendency for existing coloured (or plain) lamps to shatter or the envelope to be weakened when used outside and subject to direct impact by rain drops or in an internal environment where water droplets are present such as in tunnels, mines, inspection pits, building sites and swimming pools.

It is an object of this invention to provide a viable alternative to existing arrangements ^" in providing coloured light from plain light devices, and to that end we have investigated the possibility of materials other than of paint or lacquer type being capable of application directly onto light device enclosures _^ In doing- so, and bearing particularly in mind the inadvisability of requiring a further colouration coating step by the light device manufacturer, we came to the concept of a cover product capable of separate manufacture and later installation, over, but contacting a normal light device enclosure, pre erably removably for re-use or use " only when coloured light is required. Such cover product requires a material capable of withstanding temperatures generated at light device enclosures, typically up to 300 degrees Centigrade for incandescent

bulbs (though rather less for fluorescent tubes), and of suitable stretch and recovery, i.e. elastic, properties in order to form a cover product that will be close-fitting, possibly require significant stretch properties at least for standard bulbs. Suitable materials were found to be silicone rubbers, such as cross linked with peroxide or addition cured say by means of a platinum based curing system, which further have the advantage of being non-toxic to human skin, are non-stick to glass, and have good colour-fastness. There are so many synthetic plastics materials that exhaustive investigation of available materials, and possible special formulations, is impractical for us.

Accordingly, one aspect of this invention is an elastic form-sustaining material in a shape and structure constituting a light-transmitting cover product capable of closely fitting, preferably with some degree of stretch, over the normal enclosure of a light device, and of a desired colour (though it may be uncoloured transparent or translucent where protection against shattering or weakening of the envelope is the prime interest). The preferred stretch can be very small in percentage terms but may be differential for some- bulb shapes. The only limitations for said stretching are, in fact, mechanical in terms of

capability to fit the cover products to desired bulbs etc and in not imposing higher compressive forces than can be withstood by the bulb or tube enclosures. Typical products range from simple tubular sleeves for fluorescent tubes through tubes closed at one end for incandescent bulbs of so-called pigmy or candle type and dished covers for flared lamps such as reflective spot lamps etc to necked down balloon-like shapes for GLS lamps. Manufacture of such products, by controlled laying of material onto suitable forms is doubtless- feasible, whether by an injection moulding process .or otherwise, but" any suitable process may be used. We have, in fact ascertained that there are no difficulties in this respect, as would be expected from existing: tubular rubber- products and rubber balloons.

A ¹ preferred manufacturing process uses injection moulding techniques modified to suit requirements of the product. Maintaining wall thickness for the covers of the invention is important particularly if differential wall thicknesses are to be achieved. Variations from derived thicknesses upto 0.1mm may be tolerated but above that are undesirable, as localised weakness or localised strong coloration may result. The preferred moulding machine uses an injection

screw for forcing uncured material into the mould. A cold runner block is preferred so as to avoid curing of material that has not entered the mould. That with a slight vaccuum on the injection screw after ; introduction of a desired amount of material to the mould will inhibit curing of material that is just prior to the mould and hence reduce risks of blockage.

Mouldable material is preferably forced into the mould at around 1000 psi. That, is low by comparison 0 with conventional injection moulding techniques that use around 20,000 psi but facilitates holding together of mould parts and hence keeps wall thicknesses within desired tolerances.

Using the aforesaid silicone rubber materials, we find that installed thicknesses of up to about 50 thou (about 1.25 millimetres), preferably 30 thou (0.75 mm) or less is satisfactory for products hereof, which can be formed, with differential wall thicknesses to take account of differential stretchings for some bulb shapes.

The type of silicone rubber used in preferred embodiments of the invention has one or more of the following:

1. Hardness, preferably in the range of 30 to 50 international rubber hardness degrees (IRH).

2. High elongation at break such as 750+50% at 30 IRH or 400+50% at 50 IRH.

3. Low modulus stress when stretched, for example at 200% elongation and 50 IRH, 3 to 3.9 MPa or at 30 IRH, 1 to 2 MPA.

4. High tear strength, for example 75 + ION at 50 IRH or 25 IRH or 25 + ION at 30 IRH per standard test piece (BS Test 903).

5. Good heat ageing say upto 250 degrees C, preferably upto 300 degrees C.

Minimum wall thickness for at least part of the covers of the invention may be 0.35 mm and preferably upto 0.60 mm-, especially upto 0.50 mm and more especially upto 0.45mm. Another aspect of this invention comprehends a light device- with a cover product of the irst aspect fitted over its normal enclosure in close contact therewith.

It majr be advantageous to use a lubricant material between the cover product hereof and the light device enclosure, for example in dry solid comminuted form as applies to powder such as talc, which may be spread onto the light device enclosure or carried internally by the close fitting cover product hereof. ^• A further aspect of this invention comprises the

method or process of producing a coloured light device by fitting a stretchable cover product of the first aspect over the normal enclosure of a light device.

Weather protection can be enhanced, particularly if the cover products hereof extend onto the metal lamp cap, say of an incandescent bulb, so as to seal against the rim of an entry to a festoon or other ^• type of lampholder. An alternative, which is preferred at least for lamp enclosures that have much greater diameters than their caps, is for a subsidiary elastic sleeve-like product to butt up to, overlap onto, or be overlapped by, -the first-mentioned- cover product. A further alternative is for the basic cover product to extend or be capable of extension onto a lampholder, typically an entry neck of such a lampholder, or for a subsidiary sleeve-like- product to extend from over such a neck to over (or under) the basic cover.

Specific implementation of this invention will now be described, by way of example, with reference to the accompanying drawings, in which:-

Figure 1 shows rough sketches of variant covers; Figure 2 shows sketches of one cover and fitting to two small bulbs;

Figure 3 shows sketches of another cover and fitting to another lamp;

Figure 4 shows sketches of a further cover fitting to a further lamp and a related mould;

Figure 5 shows sketches of a standard lamp with cover and a mould; Figure 6 shows sketches of a cap-like cover indicating fitting to a lamp;

Figure 7 shows sketches of tubular covers for fluorescent tubes;

Figures 8 and 9 show variants with extension to covering a festoon lampholder entry neck;

Figure 10 shows a lamp with an extended cover; and

Figure 11 shows alternatives for a lamp and holder. Referring first to Figure 1, several types of incandescent lamp are shown specifically two designs of flared reflector type bulbs 10R, 10RS (also designated PAR 38 and DECOR SPOT as available commercially), a standard type of bulb 10L with a substantial globular part to its enclosure (designated

GLS LAMP), and two small bulbs 10P, IOC (designated

PIGMY and CANDLE) . The flared reflector type bulbs will usually be relatively large and are shown at 12R,

12RS, with cover products hereof that are of dished cap form. The small bulbs are shown at 12P, 12C with

similar cover products hereof that are of tubular form closed at one end. The standard bulb 10L is shown at 12L with a cover product hereof that is of balloon-like shape. Turning to Figure 2, versatility of a single generally tubular cover product 12A is indicated in terms of fitting both to a small lamp 10PS of the type used for signs and known as pigmy sign, and to a small round enclosure lamp 10GR of the type known as golf round. The cover product 12A is indicated as being about 51 mm in length and of tapering diameter from about 18 mm just below its closed end to about 25 mm at its open end, and further of varying wall thicknesses along its length. The purpose of the latter is to reduce variation of perceived brightness of a covered lit-up bulb, though that is not found to be great for the particular material indicated above, typically being about 2% over a range of thickness of 0.38 mm to 0.75 mm. As shown, however, a closed end thickness of 0.38 mm from 0.45 mm over the next 13 mm, 0.6 mm over a medial 32 mm and 0.45 mm over 13 mm to the open end, is found to be satisfactory, at least for the two lamp types shown.

Figures 3 and 4 shows variants (12B, 12D) on the cover products of Figure 2, effectively with same

extended to about 76 mm and 88 mm length to fit larger candle, etc, type lamps 10CX, 10CY.

Figure 4 also shows a mould 20D for the cover product 12D and is believed to be self-explanatory in terms of indicated thickness variations, also showing that the mould 20D will have a general slight flare to aid forming by injection moulding and release of its moulded cover product. Typical thickness tolerations range from plus 1 to 3 thou to minus 2 to 3 thou, and transitions will generally be smoothed/blended. A polished finish is preferred. Generally similar moulds

-for the cover products 12A, 12B will have different dimensions. .In all cases, those dimensions are to be considered as approximate and subject to alteration as may be required or desired. It is feasible to make witir a. small hole at the otherwise closed end if that assists moulding, and the indicated bead at the open end can. be very small or trimmed off if desired.

Figure 5 shows a standard light bulb 10L and cover product 12L and corresponding mould 20L from which it will be seen that the cover product 12L is made to a shape quite close to that of the bulb but slightly less in diameter (by about 1/8 inch or 3 mm) to give a good close fit. Absence of any significant bead at the open: end of the cover product may

facilitate fitting and removal of this type of cover. In addition, Figure 5 further shows a short elastic sle ^" eve 12S butting up to the open end of the cover product 10L and extending over onto the lamp cap 14 to an extent sufficient to make a resilient seal to edges 15 of the mouth of a festoon or other type of lampholder.

Turning to Figure 6, the dished cover product 12R is shown in greater detail,. actually with a reverse-angled wall formation, to assist capture of the cover product 12R on the plain, usually pearled, end of ^• the reflector _, type ^" bulb 10R." Whilst the drawing indicates a thickness of only 10 thou (0.25 mm), greater thickness could be used if more convenient. Figure 7 shows two fluorescent tubes 10F, 10F' that differ as to their diameters, and related cover sleeves 12F, 12F' that are indicated as having the same nominal ^' internal diameter as the external diameter of the fluorescent tubes. Little, if any, stretch is allowed for as friction could become great at fitting the sleeves to the tubes. However, a close fit is preferred, and that can be assured by suitable tolerance on sleeve manufacture being close and only negative from nominal. Whilst a thickness of 0.75 mm is indicated, other thicknesses could be used. Also,

sleeving can be made in any convenient length and cut to desired sizes however and whenever required.

Turning to Figure 8, a lamp bulb is shown fitted into a festoon lampholder with an extra long cover 12EL that extends beyond the entry neck of the lampholder. The alternative of Figure 9, shows a short cover 12SL on the lamp bulb and a neck cover 12N over the entry neck of the lampholder and under the lampcover 12SL. The neck cover 12N could be cut from tube as used for fluorescent tubes. It will be appreciated that other lamp bulb shapes can be similarly dealt with and that the extents of the neck and lamp covers of Figure 9 could be varied, as could overlapping or underlapping, even butting. In Figure 10 a cover 112 for an ordinary lamp bulb 110 is extra long: in order to cover not only the glass enclosure 113 of the lamp but also a major part of the lamp cap 114. The cover 112 has different wall thicknesses in different areas. For example, its top part is approximately 0.5 mm thick its neck is approxi atley 0.6 mm thick, intermediate the top and neck i.e. around the widest part of the lamp is approximately 0.45 mm thick, nearer its open end about 1.00 mm thick but with an internal bead 117 about 1.5 mm thick.

The different thicknesses allow for differential stretching requirements and the bead 117 reduces the risk of tearing of the cover.

Finally, in Figure 11 two versions a cover 212 for a lamp 210 and lampholder 214 are shown. One version 212A of the cover extends onto the holder but the other version 212B extends to enclose a part of the holder.